DotCHA: An Interactive 3D Text-based CAPTCHA

  • Suzi Kim School of Computing, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
  • Sunghee Choi School of Computing, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
Keywords: CAPTCHA, 3D CAPTCHA, text-based CAPTCHA, 3D typography, mental rotation, security, usability


We introduce a new type of 3D text-based CAPTCHA, called DotCHA, which relies on human interaction and overcomes the limitations of existing 2D and 3D CAPTCHAs. DotCHA asks users to rotate a 3D text model to identify the correct letters. The 3D text model is a twisted form of sequential 3D letters around a center pivot axis, and it shows different letters depending on the rotation angle. Because each model consists of many small spheres instead of a solid letter model, DotCHA is classified as a scatter-type CAPTCHA and resists character segmentation attacks. Moreover, DotCHA is resistant to machine learning attacks because each letter is only identified in a particular direction. We demonstrate that DotCHA is resistant to existing types of attacks while maintaining usability.


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Author Biographies

Suzi Kim, School of Computing, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea

Suzi Kim received the B.S. and M.S. degree in Computer Science from Korea Advanced Institute of Science and Technology (KAIST) in 2012 and 2016. She worked for the Daewoo Shipbuilding Marine Engineering (DSME) from Jan. 2012 to Mar. 2013 and Prezi from Apr. 2013 to Aug. 2014. She is currently working toward the Ph.D. degree in School of Computing at KAIST. Her research interests include computer graphics such as procedural and inverse-procedural modeling and geometry processing.

Sunghee Choi, School of Computing, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea

Sunghee Choi received the B.S. degree in computer engineering from Seoul National University in 1995, and the M.S. and Ph.D. degrees in computer science from the University of Texas at Austin, in 1997 and 2003, respectively. She has been working as a professor in School of Computing at Korea Advanced Institute of Science and Technology (KAIST) Daejeon, Korea since 2004. Her research interests include computational geometry, computer graphics and geometric problems in wireless sensor networks.


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